I see two different part #s listed for our ZL1s in the Kooks catalog. There is a signature series stepped 1 3/4" to 1 7/8" header and a 1 7/8" all the way. On their comparison the stepped header produced more hp/tq(maybe on a N/A SS). Which do you think is a better choice? I haven't called Kooks to ask but would love to hear the opinions here. Or should I ditch the Kooks idea and go with American racing 1 7/8" or another brand?